MDCAT Physics · Physics · Circular and rotational motion. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
For a body moving in a circle it is easier to measure the angle turned than the distance moved. Angles are measured in radians: one radian is the angle at the centre when the arc length equals the radius. Angular velocity ω is the angle turned per second, and angular acceleration α is the rate of change of ω.
The equations of uniformly accelerated motion have the same form for rotation, with θ, ω and α in place of s, v and a.
A body moving in a circle at constant speed is still accelerating, because its direction keeps changing. The acceleration points to the centre, and the net force that causes it is called the centripetal force.
Students add centripetal force as an extra force. It is only the name for the net force towards the centre, which is supplied by tension, friction, gravity or a normal force.
Answer: ω = 10π rad s−1 (about 31 rad s−1); a = 200 m s−2 towards the axis.
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